1. Field of the Invention
The present invention relates generally to a hydraulically operated friction coupling clutch, and more particularly to a technique for improved consistency in engagement respose and easier control of the clutch, irrespective of an amount of wear of friction members of the clutch.
2. Discussion of the Prior Art
There is known a hydraulically operated clutch which has a driving rotary member, a driven rotary member, a movable member for effecting frictional engagement between the driving and driven rotary members, a cylinder bore, an actuator piston slidably received in the cylinder bore and cooperating with the cylinder bore to define a pressure chamber, so that the piston is moved by a hydraulic pressure in the pressure chamber, to move the movable piston for frictionally coupling the driving and driven rotary members to each other. An example of this type of hydraulically operated clutch is disclosed in Laid-Open Publication No. 60-79024 (published in 1985) of Japanese Patent Application.
In such type of conventional hydraulically operated clutch, a distance of movement of the piston required for the piston to commence moving the movable member to start engagement of the clutch is inevitably increased due to progressive wear of the friction members of the clutch during use. This means an increase in the amount of flow of the working fluid necessary to engage the clutch, resulting in an increase in the engagement time of the clutch, or a prolonged response time of the clutch. Therefore, where the clutch is used for an automotive vehicle, the frictional coupling characteristic of the clutch upon starting of the vehicle or shifting of the transmission is changed or deteriorated as the service life of the clutch increases.
To eliminate the above drawback, there has been proposed a solution as described in Laid-Open Publication No. 60-11722, in which the engagement start position of the clutch which varies with the amount of wear of the friction members, is detected and stored in a memory. In this proposed arrangement, the clutch engagement action is controlled based on the updated data stored in the memory. However, this arrangement required a complicated control system.